I'm around 60K miles and wanted to know your opinions on whether i need to take my car in for service or try to replace the things(eg fuel filter, drive belt, cabin air filter, spark plugs) myself?

The only thing that really worries me is that i don't know if the ECU needs to be updated or anything if i change the spark plugs myself, because my DI cassette failed one time and while the tech replaced it and the plugs he reprogrammed/updated my ecu? Does anyone know if changing the plugs is as simple as just changing without anything needing to be reset?

Yep, to remove the DI just undo the 4 torx bolts and remove the connector on the right hand side (pull red part of plug out before trying to undo connector), change plugs, put DI back on (but wait 15mins to allow fluid to run to bottom of DI before starting).